The present invention relates to a keyboard switch apparatus for an electronic musical instrument.
In an electronic musical instrument such as an electronic organ, it is well-known to use a keyboard switch not only for providing key code data of a depressed key but also for detecting touch response such as a key depression timing (key on timing), a depression speed or pressure and a key off timing so as to enrich musical expressions. A typical example of a key switch of this type is described in U.S. Pat. No. 4,052,581. This keyboard switch is called a leaf switch. A pair of opposite stationary leaves are fixed to a leaf holder while a spring force is acting on the leaf switches which come close to each other. A movable leaf is fixed to the leaf holder and is located between the stationary leaves. A spacer is disposed between the stationary leaves. One of the stationary leaves is normally in contact with the movable leaf to constitute a normally closed switch, and the other of the stationary leaves is normally separated from the movable leaf to constitute a normally open switch.
When an actuator urges the movable leaf upon depression of a key, the normally closed switch is opened, and a key on signal concerning a depressed key or an electrical signal concerning a key code is generated. By measuring a period from a time at which the movable leaf is separated from the stationary leaf of the normally closed switch to a time at which it is brought into contact with the stationary leaf of the normally open switch, an electrical signal representing a key depression speed can be generated.
In a conventional keyboard switch apparatus of this type, although a distance between the free ends of the stationary leaves is kept substantially constant by the spacer, it is difficult to mount the spacer at a position substantially midpoint between the free and fixed ends of the stationary leaves. Furthermore, the stationary leaves are bent at many positions, so that a distance between the stationary leaves tends to vary. In addition, since the two stationary leaves and the movable leaf are held by a single leaf holder, assembly and replacement are cumbersome. The mounting operation of the spacer is time-consuming, resulting in high cost. When dust is attached to the contacts of the leaves, contact errors occur and degrade reliability and durability of the switch.